Pressure to use renewable energy sources is growing. One renewable energy source is the sun. Energy from the sun can be harvested by converting sunlight to electricity using a photovoltaic cell or a photoelectrochemical cell. Both such cells are commonly known as “solar cells.”
A basic photovoltaic cell includes a light-absorbing region bounded on one side by a hole-selective contact and on the other side by an electron-selective contact. When sunlight shines on a photovoltaic cell, it can be reflected, absorbed, or transmitted. Only the light that is absorbed in the light-absorbing region ultimately generates electricity. More particularly, only photons having an energy that is at least equal to the band gap of the light-absorbing region can free an electron in that region. The band gap for most photovoltaics is 1.1-1.7 eV. The selective contacts act like sinks for either electrons or holes and each contact establishes a potential gradient. The potential gradient generates a drift current.
Recently, researchers have been experimenting with three-dimensional (3d) hybrid perovskites of the form (MA)[PbX3] for use as the light-absorbing layer of solar cells (where: MA=CH3NH3+ and X═Cl, Br, or I).
High-quality films of 3d hybrid perovskites can be formed via thermal evaporation and two-step vapor or dip-conversion methods. Simpler deposition methods, such as single-step spin coating or dipcoating, can be used, but they produce lower quality films, which negatively impact solar-cell performance. Furthermore, 3d-perovskites are not stable in the presence of moisture, thereby requiring anhydrous processing conditions.